GraphicsGale does not have the eraser tool.All you have to do is painting a canvas with a background color.

GraphicsGale treats one of colors as transparent area.Layers and frames can have their transparent color.

If a transparent color of a layer is set, the area filled with thatcolor is transparent and its under layers are visible.A transparent color of a frame is applied as a transparent color of animage file which supports transparency such as a GIF.